The invention relates to a method for regenerating acidic cation exchangers, which are used, in particular as catalysts in the reaction of phenols with aldehydes or ketones to give bisphenols, in particular to give bisphenol A, with acids, with the proviso that, in the method according to the invention, these cation exchanger experience very little mechanical damage due to swelling processes during the regeneration process.
Condensation reactions of phenols with carbonyl compounds to give bisphenols with the use of acidic catalysts, in particular with the use of cation exchangers, are known (cf., for example, GB 842 209 A, GB 849 565 A or GB 883 391 A). It is also known that acidic cation exchangers which were deactivated by metal ions or were contaminated by organic by-products from the bisphenol preparation (“fouling”) can be regenerated by suitable measures. Thus, for example, EP 324 080 A describes a method for regenerating acidic cation exchangers by treatment with bases and acids. However, the aspect of the mechanical intactness of the cation exchangers is not considered at all here and there is also no information as to how such an aim is to be achieved. Moreover, the sequence of the various washes of the ion exchanger with water, base and acid is so complicated in practice that it is unsuitable in practice for industrial production, in particular for regeneration in an existing plant.
The publication RD 369008 (Database Document Number) of “Research and Disclosure” (Derwent Publications Ltd., London, UK, Database Accession Number 1995-080031) also reports the regeneration of acidic cation exchangers, a complicated sequence of a plurality of treatments with different agents, such as water, ketone, base and acid being recommended, which sequence is unsuitable for a regeneration on the industrial scale in an existing continuously operating production plant, since too many foreign products have to be introduced into the production process and have to be strictly removed again. Here too, the consequences of mechanical damage to the cation exchanger by swelling processes is not considered.
DE 2 727 866 A1 describes a relatively simple sequence of washes with phenol, water and acid, dispensing with a wash with bases. However, here too no information is given concerning the swelling of the cation exchangers with water and the possible consequences of mechanical destruction. Information about the effects of the water concentration or about upper concentration limits of water in the wash medium phenol and water or phenol, water and acid on the properties of the ion exchanger treated in this manner is absent.
The prior art sets no defined upper limits of a reliable water concentration in the phenol-acid mixture in the regeneration, compliance with which makes it possible very substantially to avoid excessive swelling and hence bursting of the cation exchanger particle. On the contrary, according to the information in DE 2 727 866 A1, on page 8, the proportion of water for a successful regeneration of the ion exchanger bed may be up to 30% by weight. Under such conditions, however, there is a very considerable danger of excessive swelling of the cation exchanger with said consequences. Thus, the stated upper limit is not suitable for achieving the object presented here.
This aspect is of considerable importance since cation exchangers which are usually also deactivated by “fouling”—i.e. by incorporation of relatively high molecular weight condensates, for example of phenol and acetone, into the polymer network of the catalyst particle—may swell during the treatment with excessively high concentrations of water to such an extent that the osmotic pressure in the ion exchanger particle contaminated with these “fouling” components may be so high that it breaks. This results in the formation of fine fractions of the ion exchanger particle which, during operation in the intended manner, not only lead to blockage of fixed-bed reactors and filters but, in downstream process stages, can also give rise to major faults due to secondary reactions, with quality problems as a result thereof.
The cation exchangers are used as a rule as flow-through particle beds. The change in the overall particle size distribution of the cation exchanger due to particle fracture can furthermore adversely affect the pressure drop characteristic in the flow-through cation exchanger bed, which leads to a larger pressure drop in the bed and possible hydraulic limitations and hence limitations in the production quantities.
It was therefore the object to provide a technically simple and economical method for regenerating deactivated acidic cation exchangers, which leaves the particle structure of the ion exchanger particle substantially intact and converts the functional acidic groups, such as, for example, sulpho groups, bonded to the polymer matrix substantially back into their acidic form.
The avoidance of mechanical damage caused in this manner is of major importance because very fine fragments of particles of the cation exchanger can give rise to considerable problems, for example due to undesired secondary reaction, blockages of plant parts or pressure drop limitations, after the regeneration of said cationic exchanger and during the operation thereof in the intended manner. The method according to the invention is applied to acidic cation exchangers which are used as catalysts in chemical reactions and which, in the course of their use, have lost a part of their catalytic activity there, so that the conversion of the reaction is insufficient. By the method according to the invention for regenerating acidic cation exchangers, deactivated in this manner, with acids, the catalytic activity thereof is increased again so that economical reuse of these cation exchangers several times in chemical syntheses is permitted. Ion exchangers regenerated according to the invention are in particular acidic, optionally also modified cation exchangers which are used as catalysts in the reaction of phenols with aldehydes or ketones to give bisphenols, particularly to give bisphenol A. Modified cation exchangers are, for example, cation exchangers which, in addition to their function as cation exchangers by, for example, acidic groups, are treated by application of further chemically active components having additional functions. Such chemically active components may be, for example, cocatalysts which have, for example, inter alia thiol functions.